The function of eosinophils in atopic conditions is unknown despite the fact that peripheral eosinophilia commonly accompanies diseases associated with hypersensitivity. Our preliminary observations indicate that extensive eosinophil degranulation occurs in atopic dermatitis. The long-term goals of this proposal are to determine the mechanisms by which eosinophil infiltration and degranulation occur in atopic dermatitis with particular attention to the hypothesis that the dermal mast cell is crucial to eosinophil participation. These goals will be approached: 1) by analyzing the occurrence of eosinophil degranulation in lesions of atopic dermatitis and determining structures upon which eosinophil granule proteins are deposited; 2) by determining whether IgE antibodies trigger eosinophil degranulation in atopic dermatitis; 3) by analyzing the relationship of eosinophil degranulation to mast cell infiltration; and 4) by investigating the occurrence of eosinophil degranulation in subsets of patients with atopic dermatitis not involving IgE mechanisms. Methods to pursue these studies include: pathologic examination of tissues by light microscopy, thin sectioning of methacrylate-embedded specimens, immunofluorescence, electron and immunoelectron microscopy; and measurement of urinary histamine and histamine metabolites by capillary gas chromatography-selected ion monitoring mass spectrometry. Quantitation of fluorescence in tissues will be accomplished with a microphotometric system attached to a Zeiss epifluorescence microscope. Information obtained from this research plan may provide diagnostic markers for certain cutaneous diseases and contribute knowledge of the pathophysiology of atopic dermatitis.